Making of acrylic ester crosslinked ethylene-propylene rubber covered press rolls



nited States Free 3,312,757 MAKING OF ACRYLIC ESTER CROSSLINKED ETHYLENE-PROPYLENE RUBBER COVERED PRESS ROLLS David G. McRitchie, Mount Pleasant, S.C., assignor to Raybestos-Manhattan, Inc., Passaic, N.J., a corporation of New Jersey N Drawing. Filed Apr. 14, 1966, Ser. No. 542,456 3 Claims. (Cl. 260-878) This application is a continuation in part of my application Ser. No. 263,103, filed Mar. 6, 1963, now abandoned.

This invention relates to the making of rubber covered press rolls used in paper manufacturing machines.

The prime object of my present invention relates to the making of rubber covered press rolls for paper manufacture which are characterized by the property of a desired high order of hardness known as semi-hard falling within the range of a Plastometer hardness of to 40 coupled with the property of high rebound value measured as Bashore resiliency falling within the range of 35 to 50%.

While the resulting rubber covered press rolls of the present invention owe their successful functions to the combined characteristics of the desired high order of hardness coupled with the high rebound value, the ease of processing of the rubber compound or formulation is also of great importance. It is desirable that the formulation of the compound possesses a relatively low plasticity for proper processability. It is therefore a further object of the invention to make rubber covered press rolls having the desired ultimate press roll characteristics referred to, in which the formulation has a plasticity in the desired low range.

The press rolls of the present invention are used as top press rolls in a number of positions or operations in the paper making process including primarily the positons of Size Press, Breaker Stack and Gloss Calender.

Size Press rolls used in the manufacture of paper consist of a pair of rubber covered rolls, one rock hard (having a 0-5 Plastometer rating) and the other semihard (having a 20-30 Plastometer rating). In paper manufacture, paper is passed through the nip of the two press rolls, where it is impregnated with starch size for enhanced printability. These press rolls as presently used in paper mills are very large, running to about 20 feet in length by 3 feet in diameter. The pressure exerted by the rolls on a sheet of paper being passed therethrough is in the order of 150 to 200 lbs. per linear inch of width.

At this Size Press stage of the paper making process, pulp wads, diflicult of being excluded, are often present in the paper sheet; and with the passage of a wad of pulp in the sheet the softer (the semi-hard) of the two press rolls is marked or dented thereby. Press rolls in this hardness range (20-30 Plastometer) are very dead, having only about 10%-20% rebound (resiliency), with the result that such rolls retain the mark or dent made therein. As a result, the sheet is correspondingly marked with every revolution of the roll. When such a mark or dent occurs, the press roll is usually removed and the whole surface thereof is reground until the depression caused by the wad is removed. This is manifestly a costly maintenance item for the paper mill involved.

The semi-hard press rolls of the present invention when used for the Size Press operation when made with a hardness range of a 20-30 Plastometer rating are characterized by having a high rebound value, in the range of 35- 50% Bashore resiliency; and such press rolls used in the Size Press stage are not prone to be marked by wads of pulp passing through the nip formed by the top and bottom press rolls. To appreciate the seriousness of such wad marks, or other indentations (caused by breaks in the sheet) one has to consider the fact that paper, or paperboard so marked is unsalable. Also, if marks do not iron out, they must be ground out; and this means shutting the machine down, and changing rolls, a time consuming and costly operation.

The position of Breaker Stack is located approximately /a of the length of the Dryer Section of the paper machine. The function here is to further densify and level the sheet. The top roll of the present invention for this position is covered with a 15-20 Plastometer hardness compound; the bottom roll is covered with a 0-5 Plastometer (Rock hard) compound. To accomplish the levelling out of the sheet, pressures of 200-300 pounds per linear inch of cover length are used. Some few wads of pulp, apparently difiicult to entirely eliminate in any paper making operation, pass through here, as well as tails (the end of a break in the sheet). Both wads and tails will mark the normal prior art top roll, the extent of which is determined by the size of the wad, or in the case of a tail, the caliper of the sheet. As with Size Press, marks in normal rolls have to be ground out. Resiliency of said normal rolls in the 15-20 Plastometer range would be of the order of 10-20% Bashore. The press rolls of the present invention compounded to have a 15-20 Plastometer range are characterized with a Bashore resiliency in the range of 35 to 50%.

The location of the Gloss Calender is just ahead of the Calender Stack on the paper making machine. The top roll used in this location is internally cooled and is generally accepted to be in the order of 10-15 Plastometer hardness; the bottom roll is chrome plated metal, and is steam heated. Pressures of from 250-400 pounds per linear inch of rubber cover face length are generally applied here. Marking of the top roll here is not so much a function of pulp wads as it is of tails, or wrinkles in the sheet. Such markings transferred from the top roll to the top side of the sheet of course makes unsalable paper. Resiliency of normal rolls in the 10-15 Plastometer range would be in the order of 10-20% Bashore. With the top rolls embodying the present invention and made to have a 10-15 Plastometer range, the Bashore resiliency or rebound also has a high level of from 35-50%.

It has been found that these rolls of the present invention for whatever position in the paper making process they occupy possess the added advantage of having longer runs than usual between the periodic regrinds necessary for proper roil maintenance. This is due to the high abrasion resistance offered by the cover stock.

In making press rolls for carrying out these objects and performances, the rubber covering of the rubber covered press rolls of the present invention is compounded from an ethylene-propylene rubber, vulcanized or cross-linked with any of a selected group of acrylic ester monomers, and more particularly in a relative proportion of these ingredients such as to accomplish the combination of characteristics referred to, such relative proportions comprising the use of the acrylic ester monomer in the range of the proportion of from 10-40% by weight, based on the weight of the ethylene-propylene rubber in the composition.

To the accomplishment of the foregoing objects and such other objects as may hereinafter appear, the present invention relates to the rubber covered press rolls as sought to be defined in the accompanying claims when taken together with the following description thereof.

Ethylene-propylene rubber commonly referred to as EPR is an amorphous or noncrystalline elastomer polymer polymerized from the monomers ethylene and propylene, using polymerization catalysts. The polymer known as EPR404 contains 43 weight percent ethylene, is vulcanizable with peroxides, with preferably a small amount of sulphur added, to stable chemical cross-links producing vulcanized products at a press cure of 320 to 360 F. over a cure time of from 30 to 40 minutes. Reinforcing fillers commonly employed in rubber technology are also effective in ethylene-propylene elastomer copolymers.

I have found that in vulcanizing or cross-linking an EPR compound with an acrylic ester monomer as described herein and particularly in the relative Proportions herein set forth, there is produced a rubber composition possessing the above referred to characteristics of a high order of semi-hardness coupled with a high rebound (resiliency) value, and a relatively low processing plasticity, all combined to the making of an elastomer' uniquely serviceable as a covering composition for the press rolls described above.

The acrylic ester monomers found most effective for the purpose are the di-methacrylates of diols such as neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, trimethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate; trimethlol propane trirnethacrylate; allyl methacrylate; and diallyl fumarate.

The EPR compound, such as EPR 404, is blended with the acrylic ester monomer, together with a filler, a suitable pigment and with preferably a peroxide vulcanization agent-(with an added small amount of sulphur); and the composition is cured for 30 minutes at 320 F. As evidenced by room temperature and elevated temperature hardness readings (Plastometer) the compounds containing the acrylic ester monomer are thermoset.

The following examples will illustrate the embodiments of the invention. The rubber coverings of the press rolls of the present invention are compounded from the formulations set forth in the examples; wherein all parts given are by weight.

' Example I This example illustrates the ingredients and ingredient proportions employed in the preparation of one of the products of the invention, as well as the physical characteristics of the resulting product. In this example the acrylic monomer is neo-pentyl glycol dimethacrylate.

Ingredient: Parts by weight Ethylene-propylene rubber (EPR 404) 100.00

Precipitated silica 40.00 Titanium dioxide 40.00 Zinc oxide 10.00 Sulphur .33 Dicumyl peroxide 12.00 Neo-pentyl glycol dimethacrylate 30.00

The precipitated silica is used as a reinforcing filler; the titanium dioxide is used as a coloring pigment; the zinc oxide is used for activating the cure; and the sulphur and dicu-myl peroxide serve as vulcanizing or cross-linking agents.

The physical characteristics of the product of the example are as follows:

Example 11 The following example illustrates a number of formulations giving a workable range of proportions of the use of the acrylic monomer and shows the effects thereof on the physical characteristics of the resulting product.

Parts by weight Ingredient:

Ethylene-propylene bb 100. O0 100. 00 100. 00 100. 00 40. 00 40. 00 40. 00 40. 00 40. 00 40. 00 40. 00 40. 00 Zinc oxide 10.00 10.00 10.00 10.00 Sulphur 33 33 33 33 Dicumyl peroxide 6. 66 4. 00 8.00 16.00 N eo-pentyl glycol dimethaerylate None 10. 00 20. 00 40. 00 The physicals of which are:

Plastometer 48 35 28 14 Rebound (Bashore resiliency) (percent) 45 39 40 43 Mooney plastieit 165 63 42 Tensile 1, 967 2, 133 1, 747 1, 687 Elongation 850 808 375 133 Shore A hardness. 65 77 82 98 Processing Very poor Poor Good Excellent The effectiveness due to the acrylic monomers used (as Well as the advantages obtained over product-s in which the acrylic monomer is absent) may be judged by the hardness produced (Plastometer and Shore A), the rebound, the Mooney plasticity, tensile strength and elongation. As known the higher the reading in Shore A durometer, or the lower the reading in Plastometer, the harder isthe material tested. Mooney plasticity is the plasticity of the compound and determines its processability; the higher the plasticity reading, the poorer generally is the processing. It will be noted that for the product in which no acrylic monomer is employed, the

processing was very poor, the high Mooney plasticity reading being 165. Optimum properties are represented by the combination of good hardness, good rebound, and low plasticity. All the products possess appropriate tensile strength and elongation. It will be noted that the product in which no acrylic monomer is used suffers not only from very poor processing but from a hardness too low comparably with the products of the present invention. It will also be noted that the higher the amount used of the acrylic monomer, the harder the product and the better the processability value, and that the peroxide cross-linking agent varies with the amount of acrylic In-onorner used.

Without the use of the acrylic monomer in the ethylenepropylene rubber compound of the present invention, a desired hardness can be induced only by the use of reinforcing fillers; but in the use thereof a point is soon reached where further filler loading cannot be accomplished due to resulting poor processing. The acrylic monomer makes the batch highly processable while increasing the hardness. In addition it tackifies the rubber compound (which is normally difiicult to tackify) to make it more serviceable for the plied-up product of a rubber covered roll. Also, the resulting rubber rolls, differing from normal rubber rolls, are not attacked by the corn starch size used.

The workable range of the acrylic monomer ingredient is a function of the formulation. In the formulations of the present example (and that of Example I), which represent a highly loaded (for hardness) base compound, it will be noted that as the content of the acrylic monomer is increased in the range of from 10% to 40%, by weight based on the ethylene-propylene rubber by weight, the compound becomes more readily processable and the hardness of the resulting product increases. Blend or mixtures having a range of the acrylic monomer up to 10% possess poor processing (high plasticity) and poor tack, as well as too low a degree of hardness (semi-hardness).

Example III Employing the ingredients set forth below, the following example illustrates formulations employing different acrylic monomers, shows the comparative physical characteristics of such formulations, and compares the same with a formulation in which the acrylic monomer is not present.

Ingredient: Parts by weight Ethylene-propylene rubber (EPR 404) 100.00 Zinc oxide 10.00 Precipitated silica 33.30 Chrome green oxide 20.00 Sulphur .33 Aldol naphthylamine .50 Titanium dioxide 20.00 Thermatomic carbon black 1.00 VaroX: 2.5 bis(tbutyl peroxy) 2.5 dimethyl hexane 6.40 Acrylic monomer 20.00

The Varox is a cross-linking agent; the aldol naphthylamine is used as an anti-oxidant; and the carbon black I claim:

1. For a paper making machine, a press roll having a rubber cover, said rubber cover being characterized by the physical properties of (a) a hardness in the semi-hard range, namely a Plastometer hardness in the range of 10 to 40, and (b) a rebound value, namely a Bashore resiliency in the range of 35 to 50%, said copolymer comprising a cured composition of ethylene-propylene rubber cross-linked with vulcanizers including an acrylic ester monomer, the acrylic ester monomer being in the range of proportion of from 10% to 40% by weight, based on the weight of the ethylene-propylene rubber in the composition.

2. The rubber covered press roll of claim 1, in which the acrylic ester monomer is selected from the group consisting of diand tri-methacrylate of diols, allyl methacrylate and dia-llyl fumarate.

3. The rubber covered press roll of claim 1, in which the said composition uncured has a Mooney plasticity in the order of 40 to 80.

and chrome green oxide are used as coloring agents.

Acrylic Monomer Plas- Bashore Mooney Tensile Elongation Shore A tometer Rebound None 61 40 119 1, 488 781 66 Neo-pentyl glycol dimethacrylate 32 40 44 1, 473 333 85 Ethylene glycol dimethacrylate 27 44 54 1, 450 266 86 Triethylene glycol dirnethacrylate 39 40 69 1, 525 400 84 Tetraethylene glycol dimethacrylate 39 37 75 1, 445 400 84 Polyethylene glycol dimethacrylate 41 37 75 1, 470 433 76 Trimethylol propane trimethaerylate 45 72 1, 350 308 86 Allyl methacrylate 39 42 78 1, 170 303 81 Diallyl fumarate 66 1, 166 200 85 The making of rubber covered press rolls of the pres- References Cited by the Examiner ent invention, the composition employed therefor, and the 40 UNITED STATES PATENTS functioning and advantages of such press rolls in the art of paper manufacture, will, it is believed, be fully ap- 3,111,500 11/1963 3 et 260 878 parent from the above detailed description thereof. It 3,125,546 3/1964 PmPer et 260878 will be further apparent that changes may be made in 30139326 7/1964 Ralnwater 260 132 .th in re nts o the com ositio an t tho f e g f P n d he m d O 4.5 MURRAY TILLMAN, Primary Examiner,

producing the rubber elastomer product Without departing from the spirit of the invention defined in the following claims.

D. BREZNER, Assistant Examiner. 

1. FOR A PAPER MAKING MACHINE, A PRESS ROLL HAVING A RUBBER COVER, SAID RUBBER COVER BEING CHARACTERIZED BY THE PHYSICAL PROPERTIES OF (A) HARDNESS IN THE SEMI-HARD RANGE, NAMELY A PLASTOMETER HARDNESS IN THE RANGE OF 10 TO 40, AND (B) A REBOUND VALUE, NAMELY A BASHORE RESILIENCY IN THE RANGE OF 35 TO 50%, SAID COPOLYMER COMPRISING A CURED COMPOSITION OF ETHYLENE-PROPYLENE RUBBER CROSS-LINKED WITH VULCANIZERS INCLUDING AN ACRYLIC ESTER MONOMER, THE ACRYLIC ESTER MONOMER BEING IN THE RANGE OF PROPORTION OF FROM 10% TO 40% BY WEIGHT, BASED ON THE WEIGHT OF THE ETHYLENE-PROPYLENE RUBBER IN THE COMPOSITION. 